An increasing number of users are utilizing network systems and services to obtain various types of information and perform various actions. In order to ensure the security of these actions, passwords, tokens, and other security mechanisms or credentials are put into place to attempt to prevent unauthorized access. For example, information for a network session might be provided to a client device in the form of a browser cookie, where a copy of the cookie must be provided with subsequent communications on the session for purposes of authentication. It is often the case, however, that a copy of the cookie and/or the information in the cookie can be obtained by other users or devices, such as by a device intercepting a communication with a copy of the cookie or causing a message to be sent to a device that includes a copy of the cookie. Any party receiving a copy of the cookie can potentially impersonate the user and/or client device by including the copy of the cookie with a subsequent request, which can lead to any of a number of undesirable results for the user or the party to whom the user was impersonated.